1. Field of Invention
This invention relates to a power module in which a power circuit section including a bus bar and a semiconductor device is disposed through an insulation layer on a heat radiation member. This invention also relates to a method for producing the power module, and more particularly relates to a power module that can be used as, for example, a power distributor for a vehicle for distributing an electrical power to a plurality of electronic units from a common power source on a vehicle, and to a method for producing the power module.
2. Description of Related Art
Heretofore, as means for distributing a power to each electronic unit from a common power source on a vehicle, a junction box has been known which constitutes a power circuit section in which a plurality of bus bar boards are laminated, and a fuse and a relay switch are incorporated on the boards.
Such junction box contains the power circuit section described above in a casing having a lower casing member and an upper casing member. In view of prevention of a short circuit, the upper and lower casing members are coupled to each other in a waterproofing manner, thereby waterproofing an interior of the casing.
Recently, in order to perform a downsizing of a junction box that distributes an electrical power to each electronic unit from a common power source on a vehicle and a high speed switching control, a power module has been developed in which a semiconductor switching device, such as an FET (field-effect transistor), is disposed between an input terminal and an output terminal. In the power module, a power circuit section is arranged on a circuit arrangement surface of a heat radiation member in order to remove a heat generated from the semiconductor. For example, see Japanese Patent Public Disclosure No. HEI 11-204700.
It is necessary to prevent a short circuit in even the power module disclosed in Japanese Patent Public Disclosure No. HEI 11-204700, just as in the case of a conventional junction box. Accordingly, a power circuit section in the power module requires a waterproof function. However, a specific structure for a waterproof function has not been disclosed yet.
Japanese Patent Public Disclosure No. HEI 11-204700 discloses that a semiconductor or the like in a central part of a circuit is transfer-molded or potted with a resin. However, even if this is a purpose for waterproof, an additional waterproof treatment must be done to prevent a short circuit between terminals projecting upwardly from a periphery of a circuit. An efficiency of production will be lowered in association with increase of such fine steps. It is impossible to easily and surely waterproof the entire power module.
In view of the above problems, an object of the present invention is to provide a power module in which a simple structure can effectively waterproof an entire power module as well as a connector, and to provide a method for producing the power module.